1. Field of the Invention
This invention is in the field of transceivers, and more particularly relates to a transceiver which is used to drive substantially square wave form signals having a high frequency onto a transmission line through a coupling transformer and of receiving through the transformer such high frequency signals transmitted by another such transceiver and a lower frequency signal having a quasi-sinusoidal wave form which signals are concurrently carried by the transmission line.
2. Description of the Prior Art
Transceivers which transmit and receive signals over a transmission line are well-known in the art. Where signals from two or more sources are to be transmitted, or carried concurrently over a single conductor, this is typically accomplished by some form of multiplexing or modulation system using a carrier signal. Applicant is unaware of any transceiver that can transmit and receive a first type of signal at one frequency over a single conductor and which can also receive a second type signal at a different frequency which is also concurrently carried by the single conductor in the absence of any modulators or demodulators, multiplexers or demultiplexers.
The environment in which the transceiver of this invention is used is a token passing local area network in which a limited number, sixty four being the maximum number in the preferred embodiment, communicate with one another over the network's transmission medium, a pair of coaxial cables. Communication between physical modules is at a frequency of 5.0 MHz with the physical module of the network having the token at any given time and being enabled to transmit Manchester encoded binary data signals at a 5.0 MHz frequency over the transmission medium to any one or all of the physical modules of the network. Each physical module must therefore have the capability of transmitting and of receiving data signals at the 5.0 MHz frequency over both cables of the network medium.
In addition, there is a requirement, particularly where the network forms or constitutes, a control system for monitoring and controlling industrial and utility plants, to time the occurrence of events with a high degree of precision. In the environment in which the transceiver of this invention is utilized each physical module includes a timing subsystem. Selected ones of the timing subsystem of the physical modules prepare and transmit encoded timing information in the form of timing signals over the networks communication medium so that the timing subsystems of all physical modules can synchronize within a desired degree of accuracy, their internal senses of time with the internal sense of the timing subsystem of the physical module which timing subsystem is designated as the master.
In the preferred embodiment, the communication medium is dually redundant; i.e., it consists of two coaxial cables. In normal operation both cables carry the same data signals. The timing subsystem designated as a master is provided with a timing subsystem driver circuit which drives quasi-sinusoidal timing signals having a frequency of 12.5 KHz onto one of the coaxial cables of the transmission medium. A second timing subsystem designated as a slave is also provided with such a driver circuit and applies timing signals onto the second coaxial cable of the dually redundant transmission medium. The length of the cables is limited to the length of substantially 1000 ft. in the preferred embodiment. For additional information on this environment, reference is made to the following concurrently filed patent applications:
1. Method and Apparatus for Synchronizing Timing Subsystems of the Physical Modules of a Local Area Network, by David L. Kirk, Application Ser. No. 682,645, filed Dec. 17, 1984, and PA1 2. Driver Circuit, by Robert L. Spiesman, Application Ser. No. 682,522, filed Dec. 17, 1984,
Both of the above identified applications are being filed concurrently with this application and are assigned to Honeywell Inc., the assignee of this application. The disclosures of the above identified applicaation are hereby incorporated by reference into this application.